The West was caught by surprise when Soviet tanks crushed the Prague Spring

Forty years ago [in August] the Soviet Union ended the so-called Prague Spring with a massive invasion of troops and tanks. Intelligence files from that era show that the largest military operation in Europe since 1945 took the West by surprise.

When it was over, Western officers, awkwardly, seemed surprised. Against their will they had to admit the camouflage hiding the march of Warsaw Pact troops into Prague had been "good," and the speed of their divisions "impressive." The way the Kremlin led units out of the western part of the Soviet Union "unnoticed" was also noteworthy. The enemy, in short, had scored a "tactical victory."

This was the verdict on Aug. 27, 1968 from NATO headquarters in Brussels on "Operation Danube" -- the suppression of the legendary Prague Spring. A week earlier, 27 divisions of Soviet Russians, Poles, Hungarians and Bulgarians -- around 300,000 men, armed with 2,000 heavy cannons -- marched into the small state of Czechoslovakia to end the experiment of "socialism with a human face." It was the largest military operation since the World War II, and the West was caught off guard.

For months, the eyes of the world had been on Prague, where a group of officials around Communist Party chief Alexander Dubcek had challenged the Soviets with new civil rights for Czechoslovakia, new press freedoms and plans for privatization. Leonid Brezhnev, General Secretary of the USSR's Communist Party, ordered a number of threatening military maneuvers in and around Czechoslovakia starting in May.

But when the maneuvers grew serious, the American, British and German governments seemed to look the other way, judging by documents from the NATO archive in Brussels as well as intelligence files seen by SPIEGEL. "Not a single evaluation" managed to predict the Soviet invasion of Prague, according to the NATO Military Committee, the alliance's highest military authority.